A conventionally known cleaning method and apparatus is used to dip a substrate or a similar object in a cleaning liquid and thus expose it to an ultrasonic wave to clean it. To clean the object's entire surface uniformly, the cleaning method is required to expose the entire surface to the ultrasonic wave. However, the ultrasonic wave is partially interrupted by a structure (e.g., a holding member for holding the object) in a cleaning tank holding the cleaning liquid, and as a result the object has a surface which is not directly exposed to the ultrasonic wave. In order to solve such a problem, various techniques have conventionally been proposed.
For example, Japanese Patent Laying-Open No. 2009-231668 indicates that an ultrasonic refraction member which can be swung is disposed at a bottom of a cleaning tank, and the ultrasonic refraction member is swung to vary a direction in which an ultrasonic wave travels in the cleaning tank. JP2009-231668 indicates that this minimizes a portion of an object to be cleaned that is insufficiently exposed to the ultrasonic wave.
Furthermore, Japanese Patent Laying-Open No. 2001-057354 indicates that a cleaning tank having an ultrasonic oscillation source provided on a bottom surface thereof has a cylindrical rod disposed on the bottom surface thereof to disperse an ultrasonic wave in the cleaning tank. The document indicates that this allows an object, or a substrate, disposed in the cleaning tank to be cleaned substantially uniformly.
However, the apparatus disclosed in JP2009-231668 is required to have a mechanical structure in the cleaning tank to swing the ultrasonic refraction member, and as a result the apparatus is complex and expensive. Furthermore, while the apparatus disclosed in JP2001-057354 allows a substrate to have a surface having a relatively large area exposed to an ultrasonic wave, the apparatus cannot adjust ultrasonic exposure in conformity to a cleaning condition, and it is thus difficult to completely entirely expose the surface to the ultrasonic wave.